Wiper blade construction for wiped film liquid processors



Sept. 18, 1962 F. E. ROBBINS WIPER BLADE CONSTRUCTION FOR WIPED FILM LIQUID PROCESSORS 2 Sheets-Sheet 1 Filed March 9, 1959 m m m0 R ME K m R F P 1962 F. E. ROBBINS 3,054,444

WIPEZR BLADE CONSTRUCTION FOR WIPED FILM LIQUID PROCESSORS FIG. 8.

INVENTOR FRANK E. ROBBINS MZ/ZW United States Patent 3,054,444 WIPER BLADE CONSTRUCTION FOR WIPED FILM LIQUID PRGCESSORS Frank E. Robbins, 311 Alexander St., Rochester, N .Y. Filed Mar. 9, 1959, Ser. No. 798,141 6 Claims. ({Jl. 159-6) This invention relates to an improved construction for a wiper for apparatus for processing liquids in thin, turbulent film form.

In recent years, devices utilizing agitated films have been widely used for evaporating and for concentrating liquids, such as, for example, orange juice. In this type of device, the liquid is caused to flow downwardly in a film over the inner surface of a cylindrical shell, and heat is applied to the outer surface of the shell, and frequently, the shell is maintained under reduced pressure. A rotor is mounted for rotation concentrically within the shell, and a plurality of vanes are mounted on the rotor. The outer edges of these vanes are disposed with a predetermined clearance from the evaporating surface. This clearance may be on the order of a few thousandths of an inch, for example.

The rotor vanes disrupt the liquid film, and impart to it a degree of turbulence that improves its thermal conductivity. Although the amount of turbulence obtained is limited, the thermal conductivity is improved, and the thermal hazard in such equipment is relatively low by comparison with pot stills, for example. For this reason, apparatus of this type is often recommended for processing many thermally sensitive liquids.

As a practical matter, however, it is extremely difficult to construct apparatus of this type in which each of the vanes has the same clearance from the evaporating surface, and in which the cylindrical evaporating surface is true. As a consequence, ordinarily one vane will carry a heavier load than the others, and this places a severe strain on the rotor bearings. Moreover, where the evaporating surface is not true, there is poor heat exchange, and burning and charting may occur. Furthermore, since the vanes are pushing a mass of liquid around on the evaporating surface, the power consumption that is required is quite high.

To overcome these difficulties, liquid processing devices have been developed in which the liquid fihn is repeatedly removed from the cylindrical evaporating surface of a dome and reapplied thereto, using wipers mounted on a rotor to remove the liquid film by a wiping action, in such a manner that the entire evaporating surface is wiped at least once with each revolution of the rotor, and the removed liquid reapplied in a different location. The wipers have been molded of synthetic plastic material, with lengths on the order of several inches, and mounted one above the other on the rotor for independent radial movement to engage the evaporating Surface uponrotation of the rotor. However, there is occasionally some difiiculty in assembling and in dismantling the stills, since essentially it is the evaporating surface that holds the wipers in place, and when the dome is removed from the rotor, there is some tendency for the wipers to fall out.

With a cylindrical evaporating surface having a diameter of about 3 feet, a rotor speed between 60 rpm. and 100 rpm. is sufficient to cause the wipers to be thrown out under centrifugal force to wipe the surface to remove substantially all of the liquid in the fihn on the wiped area. With extremely viscous liquids, or with thick slurries, however, there is often a tendency for the wipers to ride over the liquid, rather than to wipe it from the surface. This is particularly true at the lower end of the evaporating surface, where the liquid film is apt to be of greater viscosity or concentration.

One object of the present invention is to provide an improved wiper structure that will be free from any tendency to ride over the liquid and that Will provide uniform wiping action over the entire axial extent of the evaporating surface.

Another object of the invention is to provide an improved wiper structure fora wiped film processing device that is inexpensive to manufacture and that will not fall from the rotor frame when the still is being assembled or disassembled.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

In the drawings:

FIG. 1 is a part elevation, part axial section, of a wiped film processing device, that is particularly adapted for vacuum distillation, and that employs a plurality of wiper elements constructed according to one embodiment of this invention, showing these wiper elements spaced slightly from the evaporating surface for purposes of illustration only;

FIG. 2 is a fragmentary section, on an enlarged scale, taken on the lines 2-2 of FIGS. 1 and 3 looking in the direction of the arrows, and showing the Wiper element moved radially outward and engaged lightly against the evaporating surface;

FIG. 3 is a side elevation thereof, with the cylindrical shell removed;

FIG. 4 is a fragmentary section taken on the line 44 of FIG. 3, looking in the direction of the arrows;

FIG. 5 is a section taken on the line 5-5 of FIG. 3, looking in the direction of the arows;

FIG. 6 is a top plan view of a wiper element constructed according to a modified embodiment of this invention, on the same scale as FIG. 2;

:FIG. 7 is a fragmentary side elevation thereof; and

FIG. 8 is a section taken on the line 8-8 of FIG. 7, looking in the direction of the arrows.

.Referring now in detail to the drawings, 10 denotes the base of a still. The base 10 is adapted to be supported on a plurality of brackets 11 that are spaced angularly about its lower face. A generally cup-shaped dome 12 is seated on the base 10 in vacuum-tight fashion. The dome 12 is formed with a generally cylindrical surface 14 that functions as the evaporating surface of the still. A heating jacket 15 and insulation 16 are disposed around the outer surface of the dome 12, to apply heat to the liquid as it flows downwardly over the evaporating surface 14.

A rotary bearing 17 is disposed at the upper end of the dome 12, and is mounted to be driven by a motor 18 that is supported above the dome on a frame 20. A shaft 21 projects from the bearing 17 into the dome chamber, and a rotor frame 22, that has an imperforate upper surface, is secured to the shaft 21 for rotation upon rotation of the shaft. A ring 24 is secured to the top of the frame 22, and a plurality of nozzles 25 are secured at spaced locations around the circumference of the ring 24, to discharge liquid from within the ring onto the evaporating surface 14. A feed pipe 26 is connected in vacuum-tight fashion through the dome, to supply liquid to the interior of the ring 24.

The frame 22 includes a plurality of generally axially extending, downwardly depending U-shaped channels 27 that are mounted for rotation upon rotation of the shaft 21. These channels 27 are disposed with their open faces confronting the evaporating surface 14. A ring 30 of angle iron is secured to the lower ends of the channel 27, to hold the channels in alignment, and to provide a stop at the lower end of each channel. A wiper 31 is disposed in each channel 27, with its sides slidably engaged against the side surfaces of the channel. Each Wiper is formed with an elongate transverse slot 32, and

a pin'34 is secured through the side portions of the channel 27 and through the slot 32, to hold the wiper 31 against axial movement, and to permit limited radial movement relative to the evaporating surface 14.

The base is generally saucer-shaped. A generally cylindrical wall member 35 is secured to the bottom of the base 10 to provide outer and inner compartments for liquid storage, as will presently be described'in greater detail. A tubular condenser 36 is mounted on the base 10, and is disposed concentrically of the frame 22, with sufficient clearance to permit rotation of the channels 27. Cooling water inlet and discharge pipes 37, 38 respectively, are connected to the condenser 36 through the base 10 in vacuum-tight fashion. A large bore conduit 40 is connected through the base 10 to the interior of the still, substantially concentrically of the evaporating surface 14 and within the condenser 36, for connection to a vacuum system for maintaining the still under vacuum.

Referring now particularly to FIGS. 2, 3, 4 and 5, each wiper 31 is formed with a plurality of projecting portions or members 42 that are generally in the shape of parallelepipeds. The axially extending sides of these parallelepipeds are aligned and coplanar, .and their other sides .are disposed in parallelism. The projecting portions 42 are spaced apart from each other to provide slots 44 therebetween. Each projecting portion or member 42 is milled out to provide a cavity or recess, denoted generally at 45 (FIG. 4), on substantially a di agonal line from the upper part of its upright leading edge 46 almost 'back to the lower part of its trailing edge. Thus, each member 42 is formed at its radially outer end with a blade-like web portion that has its leading edges 46 disposed to engage liquid in a film on the surface 14, to remove the liquid from the surface upon movement of the wiper 31 over the surface. Each bladelike web portion has radially outer and radially inner faces. The outer web face is disposed to engage against and to slide over the surface 14. The inner web face is formed and disposed to permit the flow of removed liquid thereover. The thickness of the blade-like web portion, that extends between these outer and inner faces, gradually decreases in height away from its leading edges 46 (FIG. 3).

In operation of this device for vacuum distillation, the motor 18 is driven to rotate the shaft 21 and the rotor frame 22. Feed liquid is-supplied through the line 26 to flow into the ring 24 and be distributed through the nozzles 25 onto the evaporating surface 14. As the frame is rotated, the nozzles 25 traverse a generally circular path, and spray the feed liquid around the upper part of the evaporating surface 14. The liquid immediately forms into a film and begins to flow downwardly over the evaporating surface 14 under the influence of gravity.

The pipe 40 is connected to a vacuum system and the interior of the still is evacuated to any desired pressure. For distilling vitamin A from fish oil, for example, the still pressure could be maintained at 10 microns or lower. -For purifying various esters for use as plasticizers,

high vacuum on the same order can be used advanta-- geously. For concentrating orange juice, however, and for similar applications where high vacuum is necessary, pressures on the order of one or two mm. may be employed. Heat is applied to the liquid in the film as it flows over the evaporating surface 14, from the electrical heating unit 15.

As the frame 22 rotates, in a clockwise direction relative to FIG. 2, at speeds on the order of 60 to 100 rpm, such as, for example 72 r.p.m., the wiper elements 31 are thrown outwardly under centrifugal force so that the radially outer faces of the projecting portions 42 engage the evaporating surface 14. The knife-like leading edges 46 of each projecting portion 42 engage the liquid in the film and remove it from the evaporating surface. The liquid flows into the milled-out recesses 45, and the pressure that is exerted by the removed liquid forces the radially outer faces of the projecting portions 42 tightly against the evaporating surface 14, to insure good contact with the evaporating surface, with substantially complete removal of all liquid thereon.

The removed liquid is passed down through the recesses 45 and through the slots 44, and is discharged back onto the surface 14 with downwardly accelerated motion over the surface. The wipers continuously remove the liquid from the evaporating surface, mix up the removed liquid, accelerate it downwardly, and discharge it back onto the surface at an axially downward location from where it was removed, to flow downwardly again in a fresh film. The successive removal and reapplication of the liquid to the evaporating surface imparts a high degree of turbulence to the liquid and imparts to it the thermal conductivity characteristics of a turbulent liquid. Moreover, fresh surfaces of the liquid are continuously exposed so that heat exchange and vaporization are extremely eflicient. In addition, the wipers exert a positive pumping action that forces the liquid through the still, and this is a particularly advantageous characteristic for handling heavy viscous liquids.

Vapor that is evaporated from the liquid on the evaporating surface 14 is condensed on the condenser 36, and runs down on the condenser into the inner compartment of the base 10, within the wall 35, from which it each projecting portion 42 can make good sliding contact with the evaporating surface, the wipers 31 preferably are made from a flexible, resilient synthetic plastic material, such as, for example: polytetrafluoroethylene, which may be advantageously combined with graphite, or boron nitride; or polyvinyl chloride, polyethylene, or nylon, containing a filler and modifier such as, for example, graphite, boron nitride, or molybdenum disulphide, or some combination of these materials; and the like. These materials can be made suitably flexible so that the radially outer faces of projecting portions 42, at different locations along the axial extent of a given wiper 31, can move to different radial distances from the axis of rotation of the evaporating surface 14, to permit .eflicient wiping action even though the evaporating surface 14 may not be a perfectly true cylindrical surface. To improve the flexibility of the wipers, transverse cuts, generally denoted at 47 (FIG. 5), can be made from the radially inner surface of the wiper almost to its radially outer surface. 7

The contact faces of the projecting portions 42, that engage the evaporating surface 14, are arranged so that the highest part of the leading edge of one projecting portion is disposed axially above the lowest part of the trailing edge of the superjacent projecting portion. Thus, a plane that is passed perpendicular to the axis of the evaporating surface 14 will always intersect at least one face of a projecting portion 42. This arrangement of the faces of the projecting portions 42 insures that every part of the evaporating surface 14, opposite the wipers 31, is wiped by each wiper. In other words, no part of the evaporating surface passes unwiped between the projecting portions of any wiper.

' Referring now to FIGS. 6, 7 and 8, according to one modified form of the invention, the wiper comprises a metal spine 50 that has substantially the same length as the axial extent of the evaporating surface 14. The spine 50 has a generally rectangular cross-section and its lateral sides are slidably engaged against the sides of the channel 27. The radially outer face of the spine 50 is formed with a plurality of inclined recesses 51 (FIGS. 7 and 8) that are milled or cast in parallelism, to provide a plurality of parallel shoulders 52. A bore 54 is formed in a generally radial direction, relative to the evaporating surface 14, through the spine 15, to communicate with each recess 51. The centers of the bores 54 are aligned axially of the evaporating surface 14. A shaft 55 is slidably engaged in each bore 54, with its ends projecting from the ends of the bore. A retainer 56 is secured to the radially inner projecting end of the shaft 55, to limit radial outward movement of the shaft. A contact block 57 is secured to the projecting radially outer end of the shaft 55. The contact blocks 57 are slidably seated in the recesses 51, and their upper and lower sides are disposed in parallelism and are inclined at an angle to a plane that is perpendicular to the axis of the evaporating surface 14. The vertical leading and vertical trailing edges of the contact blocks 57 are aligned and extend axially relative to the evaporating surface 14.

The spine 50 is formed with a transverse slot 32, and a bolt 34, that is secured to the channel 27, secures the spine 50 in the channel 27 against movement in any direction.

Preferably, the blocks 57 are milled out, as were the projecting portions 42 in the embodiment shown in FIGS. 2 through 5 inclusive, to provide cavities 45' (FIG. 7) into which removed liquid is directed in operation of the device.

When wipers of the type shown in FIGS. 6, 7 and 8 are employed, as the channels 27 are rotated, the spines 50, that are mounted therein, are held rigidly and do not move radially. However, the contact blocks 57 are mounted for sliding movement, and under centrifugal force, are free to move radially outwardly to engage the evaporating surface 1 Since each contact block 57 is free to move radially independently of the other contact blocks on a given spine 50, uniform wiping action is obtained even where there are minute deviations from true in the evaporating surface 14. The blocks 57 are free to move radially outward to the full extent permitted by their respective retainers 56, which is, by design, a far greater distance than any deviations from true in the surface 14.

The spine 50 can be made from cast metal, such as cast aluminum, or from a cast plastic material, or from any other convenient, rigid material. The contact blocks 57 preferably are formed from polytetrailuorethylenegraphite compositions, or like materials, such as those previously described, that are reasonably strong, heat resistant, and somewhat self-lubricating.

Various modifications of the invention will occur to those skilled in the art, that are nevertheless within the teachings of this invention. For example, referring to the embodiment of the invention illustrated in FIGS. 6, 7 and 8, instead of employing a spine with milled out recesses in which the contact blocks seat, so that the contact blocks are given a large amount of support in operation of the device, I can employ a spine having a smooth radially outer face, and that is formed with square bores in which are seated square shafts, to the radially outer ends of which the contact blocks are secured. The square shafts then serve both to secure the contact blocks slidably to the spine, and to hold the contact blocks at the predetermined desired orientation.

While in the illustrated embodiments of the invention I have described the wipers as being shaped to impart to the removed liquid a motion having a component in axially downward direction, where it is desirable, the wipers can be shaped to impart an axial component to the removed liquid in an upward direction, to prolong the time of residence of the liquid on the evaporating surface.

Alternatively, the wipers can be shaped to impart substantially no axial component to the removed liquid, so that wiper action does not involve any pumping effect, but simply a redistribution and mixing effect. Moreover, the contact faces of the wipers need not be in the form of parallelograms, but could be triangular, for example. Triangular faced blocks, that have leading edges of reduced thickness and that are of gradually increased thickness at their trailing edges, provide a ploughing action that can be very effective for many viscous, heavy liquids; and, at the same time, improved contact with the evaporating surface is obtained because the removed liquid tends to force the blocks against the evaporating surface by reason of centrifugal force.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. In an apparatus for processing liquid in an interrupted, agitated film that is supported on and that flows downwardly over an internal surface of revolution that has an upright axis, an improved wiper that is adapted for rotary movement relative to said axis and over an axially-extending portion of said surface, for removing the liquid film from said surface at a plurality of axiallyspaced locations thereon, collecting the removed liquid adjacent said locations, and returning the removed liquid to said surface at different locations respectively than those from where removed, said wiper being formed with an elongate body portion that is adapted to be mounted to extend axially of said surface, a plurality of members projecting in one direction from said body portion and radially outward relative to said axis, each of said members being formed with an end portion, at its end remote from said body portion, that includes a blade-like web portion that has one edge that is disposed to engage liquid in a film on said surface to remove it from said surface upon movement of said wiper over said surface and that also has radially outer and inner faces, said outer web face being disposed to engage against and slide over said surface of revolution, and said inner web face being formed and disposed to permit the flow of removed liquid thercover in such fashion as to tend to press said outer web face against said surface of revolution, said members and their respective end portions being substantially uniformly spaced apart lengthwise of said body portion and axially of said surface of revolution.

2. An improved wiper in accordance with claim 1 wherein said members have sections in planes perpendicular to their projecting direction that, exclusive of said end portions, are substantially triangles of substantially uniform size, shape, and orientation.

3. An improved wiper in accordance with claim 1 wherein said body portion is articulated to permit the wiper to conform to the surface of revolution despite differences in the diameter of the surface of revolution along the axial extent thereof.

4. An improved wiper blade in accordance with claim 1 wherein said body portion comprises a rigid spine that is substantially coextensive with the axial extent of said surface of revolution, and that is formed with guide means, and wherein said members comprise separate blocks that are mounted independently of each other on said spine and for sliding guided engagement with said guide means at a constant orientation relative to Said spine.

'5. In an'apparatus for processing liquid in an interrupted, agitated film that is supported on and that flows downwardly over an internal surface of revolution, that has an upright axis, an improved Wiper that is adapted for rotary movement relative to said axis and over an axially-extending portion of said surface, for removing the liquid film from said surface at a plurality of axiallyspaced locations thereon, collecting the removed liquid adjacent said locations, and returning the removed liquid to said surface at different locations respectively than those from where removed, said Wiper being unitary and comprising a synthetic plastic material, and being formed with an elongate body portion that is adapted to be mounted to extend axially of said surface, said wiper also being formed with a plurality of members projecting in one direction from said body portion and radially outward relative to said axis, each of said members being formed with a face, at its end remote from said body portion, that is disposed to engage against and to slide over said surface of revolution to remove liquid from the engaged areas thereof, said members being substantially uniformly spaced apart lengthwise of said Wiper body portion and axially of said surface of revolution to provide slots therebetween to receive removed liquid to return it to said surface of revolution, said body portion being partially transversely severed at spaced locations along its length to give it articulation to permit the projecting members at different locations along its length to conform to and engage the surface of revolution despite differences in the diameter of the surface of revolution along the axial extent thereof.

6. In an apparatus for processing liquid in an interrupted, agitated film that is supported on and that flows downwardly over an internal surface of revolution that has an upright axis, an improved wiperthat is adapted for rotary movement relative to said axis and over an axially-extending portion of said surface, for removing the liquid fihn from said surface at a plurality of axiallyspaced locations thereon, collecting the removed liquid adjacent said locations, and returning the removed liquid to said surface at different locations respectively than those from where removed, said wiper being unitary and comprising a synthetic plastic material, and being formed with an elongate body portion that is adapted to be mounted to extend axially of said surface, a plurality of members projecting in one direction from said body por-' tion and radially outward relative to said axis, each of said members being formed with an end portion, at its end remote from said body portion, that includes a Web portion that has one edge that is disposed to engage liquid in a film on said surface to remove it from said surface upon movement of said wiper over said surface and that also has radially outer and inner faces, said outer web face being disposed to engage against and slide over said surface of revolution and said inner web face being formed and disposed to permit the flow of removed liquid thereover in such fashion as to tend to press said outer web face against said surface of revolution, said members and their respective end portions being substantially uniformly spaced apart lengthwise of said wiper body portion and axially of said surface of revolution to provide slots therebetween to receive removed liquid to return it to said surface of revolution, said body portion being partially transversely severed at spaced locations along its length to give it articulation to permit the projecting members at different locations along its length to conform to and engage the surface of revolution despite differences in the diameter of the surface of revolution along the axial extent thereof.

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